1. Field of the Invention
The present invention relates generally to the mixing of constituents in a stream of material and pertains, more specifically, to mixing devices for placement in a stream of material to effect mixing of constituents in the stream with lower shear and higher efficiency.
The mixing of constituents in a stream of material very often is carried out as the stream flows along a conduit, such as in a screw-type pump assembly commonly employed in extrusion and injection molding applications, as well as in other pipes and pipe-like material transport conduits. For example, in the extrusion of synthetic polymeric materials, often two or more constituents are fed together to be mixed as the material is moved along in a stream through an extruder in which a shearing action between a rotating extrusion screw and the material, which accomplishes both melting and pumping of the material to deliver a melted stream of material, also is relied upon for mixing the constituents in the material. While such an extrusion process is considered to be an excellent process for high shear melting, the extrusion process is not regarded as a highly effective mixing process. In particular, where the constituents exhibit dramatically different viscosities, or where an attempt is made to mix small quantities of a constituent uniformly into a matrix of another constituent, extrusion processes have lacked effectiveness.
2. Description of the Related Art
Efforts to increase the effectiveness of mixing constituents in a stream of material in a plasticating extruder have led to an increase in the shear of the material in the stream. Devices which raise the shear in a stream of material do provide increased mixing; however, any such improvement in mixing is accomplished at the cost of higher shear and higher material exit temperatures, leading to deleterious degradation of some materials. Attempts at low shear mixing often result in merely splitting the material flow into multiple flow streams, rather than effecting thorough mixing, due to the absence of the turbulent action required for more effective mixing.